Both are the same bcz both have almost same specifications but I like to prefer you for f1s bcz its price is less than f1 plus bt I have use both of them and I like f1plus bcz of its looks and its latest price is Rs. 24, 875 so if you want to buy oppo f1 plus so I prefer you to buy it from amazon.in and here also available f1s upgraded version with 4 gb ram n 64 gb rom which cost is only Rs. 18, 990
for buy OPPO F1 PLUS click here https://amzn.to/2lmU1IE
for buy OPPO F1s with upgraded version click here https://amzn.to/2ln86pN
both links are of amazon.in